1. Field of the Invention
The present invention relates to the alkylation of paraffinic hydrocarbon feed stocks. More particularly the invention relates to a process for wherein the olefin feed is produced by the oligomerization of propylene and isoolefins. More particularly the invention relates to a process wherein a portion or all of the traditional isobutane paraffin feed/recycle is passed through the oligomerization reactor to act as a heat sink to remove part of the heat of reaction.
2. Related Information
U.S. Pat. No. 6,995,296 discloses a process for the alkylation of alkane with olefin or olefin precursor such as an oligomer of tertiary olefin comprising contacting a liquid system comprising acid catalyst, isoparaffin and olefin in concurrent downflow into contact in a reaction zone with a disperser mesh under conditions of temperature and pressure to react said isoparaffin and said olefin to produce an alkylate product. Preferably, the liquid system is maintained at about its boiling point in the reaction zone. Unexpectedly, the olefin oligomers have been found to function as olefin precursors and not as olefins in the reaction. The olefin precursor is preferably an oligomer comprising C8 to C16 olefins corresponding to oligomer prepared from C3 to C5 olefin. In a preferred embodiment the oligomer has 6 to 16 carbon atoms and corresponds to oligomers which are prepared from C4 to C5 olefins. Instead of the expected reaction between the oligomer and the isoalkane, the oligomer is cracked into its olefin components which react with the isoalkane on a molar basis.
The great advantage of the using oligomer olefin precursors for the paraffin alkylation is that although acid alkylations are extremely exothermic and require substantial refrigeration to maintain the reaction temperature in optimum range to prevent side reactions, the present reaction of the oligomers with the isoalkane to produce the alkylate in the same yields required less refrigeration making the process less expensive for the same yield of useful product. The oligomerization process produces a heat of reaction that does not require the magnitude of heat removal as in the cold acid process.
The widest use of the paraffin alkylation is for the preparation of a C8 gasoline component. The feed to this process is usually a C4 olefin component and tertiary butane in a “cold acid” reaction usually with sulfuric acid or HF acid.